[keycloak-dev] Refresh tokens no longer reusable

Refresh tokens are no longer reusable. This is done by setting the client sessions timestamp when a new refresh token is issued. If the refresh tokens iat value is less than the client sessions timestamp it's not permitted. If anyone has time I'd appreciate a review of the changes: https://github.com/keycloak/keycloak/pull/1732 For anyone that runs into issues with this policy there's an option to disable it in the admin console in the realms token settings. This does not apply to offline tokens (at least yet). We need to add it to offline tokens as well though as it's even more important for those. There's two problems with offline tokens though, firstly the setTimestamp is not permitted on offline client sessions. Secondly if we allow setting it we would have to persist it, unless someone can come up with something clever.